In a hammer rail device for an upright piano, hammers for striking strings are supported by hammer shanks that freely turn, and after striking a string, the striking hammer turns in a direction opposite to the string due to inertia force. The movement of the hammer for striking a string is stopped by collision of the hammer shank with a hammer rail. At this time, to prevent collision noise, etc., from being generated by the stopping of the hammer shank, a hammer cushion made of a material such as felt is attached to the contact surface of the hammer rail.
With the above-described structure of the piano action, due to great inertia of the hammer, when the hammer shank collides with the hammer cushion and rebounds, in a case of playing by repeatedly striking a key at an extremely high speed, the hammer rebounding position is not stable, so that an idle strike (producing no sound) may occur, and this hinders good performance.
Therefore, to reduce the coefficient of restitution on the hammer rail and absorb the motion energy of the hammer shank at the time of collision, for example, as shown in Patent Literature 1, a structure was proposed in which the hammer cushion made of urethane, etc., is formed as a material with shock absorbing characteristics, and the surface of the hammer cushion is provided with a cushion guard with a slit for absorbing vibration caused by hammer shank collision.